Download Lecture 4, Fri 10/1/99 -

The cell cycle
Genetics 371B Lecture 4
1 Oct. 1999
The structure of DNA
Backbone
Pairing
5'
3'
3'
A
G
T
C
T
T
C
A
G
A
phosphate
ribose sugar
5'
What holds the helices together?
Length measure (double-stranded DNA):
Human genome:
What are alleles?
The cell cycle
DNA replication
A C C A T C G A
T G G T A G C T
C
G
A
T
T
A
G
C
A
T
C
G
G
C
G
C
Cell division:
What happens to the chromosomes depends on
the goal of the division
to make more “vegetative” cells:
to make gametes:
Mitosis – Partitioning replicated chromosomes
Good
Bad!
or
The problem: Partitioning replicated chromosomes
so that each daughter cell gets one copy of each
chromosome
The solution
After replication of a chromosome…
hold the two sister chromatids together
target them to opposite poles
then separate the sisters
centromere
replication
A convenient
representation… remember
that chromosomes don’t
condense and take on this
form until Prophase (the
start of mitosis)
sister chromatids
At Metaphase . . .
Chromosomes line up at cell’s “equatorial plate”
Mechanism? Spindle fibers exerting tension on
kinetochores
Once all the chromosomes are lined up…
Anaphase
Telophase
What kinds of defects would make mitosis go haywire?